Anticorrosion agents for metal surfaces that include an acidic aqueous solution of fluoro complexes have long been known. They are increasingly employed as a replacement for chromating processes which, due to the toxicological properties of chromium compounds, are less and less used. Generally, solutions of fluoro complexes of this type contain additional anticorrosion agents that further improve corrosion protection and paint adhesion. Nevertheless, different attempts have been made in the prior art to passivate metal surfaces and thereby to condition metal surfaces for the application of further coatings.
WO 00146310 for example discloses water based compositions suitable for the corrosion-resistant treatment of metal surfaces, wherein the compositions are composed of condensable amino-functional silanes and polysilanes. According to this teaching, these types of compositions are to be applied on the metal surface and dried thereupon.
JP 56125464 relates to the formation of wear-resistant coatings on metal surfaces based on curable compositions that are composed of organosilanes and silane-functional epoxy resins.
EP 2284234 A1 teaches a pretreatment for the temporary corrosion protection of metal coils based on condensed organosilanes that additionally improve the deep drawing properties of the as-treated coils. In this respect such metal treatment solutions are disclosed that contain a mixture of organosilanes that are at least partially comprised of amino-functional organosilanes, and diols of polyethers, polyesters and/or polycarbonates.
EP221637 discloses corrosion-resistant thin coatings based on aqueous compositions of silicates and hydrolyzable organosilanes, and which are suitable for high-temperature applications. These compositions have a low volatile organic content.
EP1433877 teaches aqueous compositions for the passivation of metal surfaces suitable for the application of an organic electrocoating. The compositions disclosed therein are mixtures of an amino-functional organosilane and water soluble compounds of the elements Zr, Ti and/or Hf, whilst an amount of dissolved fluorides is mandatory.
Despite these manifold compositions for the corrosion-resistant treatment of metals, which are already known in the prior art, there still exists a need to further improve the properties of the passivation layer conferred to the metal surface in the processes of the prior art. Especially, there is a need to establish stable water-based compositions based on organosilanes which are capable of efficiently passivating metal surfaces and which contain only small amounts of transition metal elements.